WASHINGTON (Reuters) - A Department of Justice survey released on Thursday on criminal victimization in the United States showed a drop in violent crimes rates from 23.2 victims per 1,000 people in 2013 to 18.6 per 1,000 people 2015.

The survey by the Bureau of Justice Statistics, an agency of the Justice Department, found no statistically significant change in the rate of violent crime, which includes rape, assault and robbery, between 2014 and 2015.

Rape and sexual assaults increased from 284,350 in 2014 to 431,840 in 2015, the survey found.

The study was conducted by the Justice Department's Bureau of Justice Statistics, which collect information on nonfatal crimes by surveying U.S. households.

Since 1993, when the survey began, violent crime rates have dropped by nearly 76 percent, and the rate of nonfatal gun violence has declined from 7.3 victims per 1,000 people to 1.1 victims.

Separately, the FBI's Uniform Crime Reporting publication released last month found that crime rates had risen in 2015.

John Pfaff, a law professor at Fordham University, said the two surveys use different metrics and one is not necessarily more accurate than the other.

The Justice Department's survey does not mean the FBI's report is wrong, Pfaff said, but it provides "yet another reason to view claims that crime is clearly rising with caution, and to make sure we do not overreact in response."

Homicide rates have increased in some U.S. cities, including in Chicago where nearly 80 people were killed mostly due to gun violence in August, the most violent month in the city in 20 years.